Ferromagnetic core with an adjustable air gap



Nov. 28, 1967 E. PADDISON ETAL 3,355,689

FERROMAGNETIC CORE WITH AN ADJUSTABLE A'IR GAP Filed June 28, 1965 U DOL G gginr -g E CLEARANCE-HOLE I 24 BEARING 25 COLLAR FIG.2 v 22 22 v a(k O O FIG.3

United States Patent Ofiice 3,355,689 Patented Nov. 28, 1967 3,355,689FERROMAGNETIC CORE WITH AN ADJUSTABLE AlR GAP EIIC lfaddison and GordonJohn Lally, Staflord, England, assrgnors to The English Electric CompanyLimited, London, England, a British company lfiled June 28, 1965, Ser.No. 467,263 Claims priority, application Great Britain, July 3, 1964,27,512/64 8 Claims. (Cl. 336-234) This invention relates toferro-magnetic cores.

According to a feature of the present invention such a core comprises aplurality of first laminations provided with first-shaped through-holesin alignment and normal thereto and a plurality of second laminationsprovided with second-shaped through-holes in alignment and normalthereto are arranged alternately one with another, or in alternategroups, the said first-shaped through-holes and the said second-shapedthrough-holes overlapping one another and arranged so that anadjusting-tool may be inserted through these holes for engagement witheither or both of the said first and second laminations whereby toeffect on rotation, about an axis fixed in space and normal to thelaminations, relative movement of the said first and second laminationsin a predetermined direction.

According to another feature of the present invention the first-shapedand the second-shaped holes are similar triangularly shaped holes, theseholes being arranged in a complementary and overlapping manner so thatan adjusting-tool may be inserted to engage each hole at the apexwhereby rotation of the adjusting-tool induces relative motion of thefirst and the second laminations by engagement with both first andsecond laminations.

According to another feature of the present invention the first-shapedholes are clearance holes and the secondshaped holes are slots, theadjusting-tool being inserted through the first-shaped holes to engageonly the secondshaped holes;

Preferably, the core has first and second outer frame members disposedat either side of the core each provided with a bearing hole forsupporting the adjusting-tool and defining its axis of rotation.

According to another feature of the present invention the core has anair-gap disposed so that rotation of the adjusting-tool efiects a changein the air-gap reluctance. Preferably the air-gap is displacedsymmetrically in the core and the laminations are arranged to each havea first-shaped hole and a second-shaped hole for enabling thelaminations to be readily used as either a said first or a said secondlamination.

According to another feature of the present invention the first andsecond laminations may be generally F- shaped.

According to another feature of the present invention the adjusting-toolhas an outer collar arranged to engage the bearing hole in one of theouter frame members, the collar acting as a bearing for an inner shaft,lateral movement of the inner shaft with respect to the collarpermitting the adjusting-tool to be used for various laminated corethicknesses.

A laminated core according to the invention will now be described by wayof example and with reference to the accompanying drawing in which:

FIG. 1 shows a pictorial view-of a laminated core;

FIG. 2 shows a pictorial view of an adjusting-tool;

FIG. 3 and FIG. 4 shows F-shaped laminations for use in the core;

FIG. 5 shows an E-shaped lamination together with a T-shaped laminationfor use as an alternative in the core.

Referring now to the drawing, a laminated core 11 (FIG. 1) comprisessets of F-shaped laminations (FIG. 3) clamped between outer framemembers 12 and 13 by four clamping bolts 14 passing through thelaminations. The outer frame member 12 has clearance holes 15 and 16 andthe outer frame member 13 has guideholes (not shown) on the same axes asthe clearance holes 15 and 16; each outer frame member has lowercircular holes 17 and upper slotted holes 13 for the clamping bolts 14.The core has an air-gap 19.

The sets of laminations are an upper left, a lower left, an upper rightand a lower right set of laminations and are interleaved with oneanother. Slots 20 of the upper left set of laminations are overlapped byclearance holes 21 of the lower left set of laminations and theclearance hole 16. Similarly, slots 20 of the upper right set oflaminations are overlapped by clearance holes 21 of the lower right setof laminations and the clearance hole 15. Clamping bolts 14 pass throughholes 22 in each lamination and holes 17 in the frame members therebyaligning each lamination to form sets of laminations. The air-gap 19 isformed between a surface 23 of each of the laminations.

Movement of the slots 20 of the upper sets of laminations with respectto the clearance holes 21 of the lower sets of laminations effectsair-gap adjustment, varying the length of the air-gap 19.

An adjusting-tool (FIG. 2) machined at one end to form a clearance holehearing has a collar which slides on a shaft 24. At a remote end of theadjusting-tool there is a guide-hole bearing disposed on the same axisas the shaft. A surface 25 between the remote end of the adjusting-tooland the shaft is shaped eccentrically with respect to the axis of theshaft. The adjusting-tool may be inserted into the clearance holes 15and 16 with the remote end bearing in the said guide-holes and thecollar bearing on the hole 15 or 16, and is thus supported for rotationby the outer frame members 13 and 16. The surface 25 engages in theslots 21) to effect adjustment of the'air-gap 19 on rotation of theadjusting-tool. The slotted-holes 18 allow the upper sets of laminationsto move only in a vertical direction as seen in the drawing.

In operation, the laminated core is built-up round an electric coil (notshown) to form an electromagnet. Calibration of the electromagnet iseffected by applying and measuring a voltage and a current to the coiland simultaneously adjusting the air-gap as desired using adjustingtoolsas described. The clamping bolts are then tightened to maintain adesired calibration of the electromagnet.

As an alternative, the F-shaped laminations of FIG. 4 may be arranged insets of laminations in a manner as described above to form the core buthave triangular holes for effecting adjustment of the air-gap. Anadjusting-tool suitably and symmetrically shaped is used for air-gapadjustment, both upper and lower sets of laminations movingsimultaneously with respect to the axis of rotation of theadjusting-tool. If the lower set of laminations are restrained by outerframe members as in the core described the axis of the adjusting-toolwill move With respect to the outer frame members and requires nosupport.

As another alternative, E-shaped and T-shaped laminations (FIG. 5) maybe arranged alternately and complementarily to form the core. Rotationof an adjusting tool eifects adjustment of the air-gap by directinteraction with the E-shaped laminations only; the T-shaped laminationsare constrained or moved, according to theirposition in the core, by theclamping bolts in conjunction with the E-shaped laminations. TheE-shaped laminations may have triangular-holes instead of clearanceholes and slots shown and provide adjustment of the air-gap in the samemanner as the F-shaped laminations in FIG. 4.

Adjustment of the air-gap may be effected by a single adjusting-tool ortwo adjusting-tools acting together. Further, with modified outer framemembers a single adjusting-tool may enter the core either throughclearance hole 16 for example, or from the opposite direction; that is,from the opposite direction the tool will pass through clearance holes21 in the upper right set of laminations to engage slots 20 in the lowerright set of laminations, appropriate clearance and guide-holes beingprovided in the modified outer frame members.

The invention is in no way limited to symmetrical cores. It will beappreciated that in the core 11 the upper sets of laminations must haveslotted holes 20 but need not have clearance holes 21. Similarly, thelower sets of laminations require only clearance holes 21. The shapes ofupper and lower sets need not be the same but slotted holes of one setof laminations must be overlapped by clearance holes of another set oflaminations throughout desired adjustment of a variable reluctanceportion of the core by relative movement of the one set of laminationswith the other set of laminations.

For cores whose outer limbs and centre limbs are the same width theholes in the laminations preferably do not exceed half the width of thelimbs otherwise undesired saturation may occur in the region of suchholes.

What we claim as our invention and desire to secure by Letters Patentis:

1. A ferro-magnetic core of stacked laminations in combination with anelongated tool, said stacked laminations being movable relatively to oneanother by said elongated tool which is rotatable about its longitudinalaxis and has an offset portion for effecting relative movement betweenthe laminations, said core com-prising first laminations each definingan aperture and all being identical in shape and size, and

second laminations, interleaved with the first laminations, eachdefining an aperture, and all being identical in shape and size, thefirst laminations cooperating with the second laminations to define anair gap for the core,

locating means for disposing the first laminations such that all oi itsapertures are in alignment and for disposing the second laminations suchthat all of its apertures are in alignment, the apertures of the firstlaminations partially overlapping the apertures of the secondlaminations to define a through hole in the stack for receiving saidtool to enable the first laminations to be moved relative to the secondlaminations to adjust the width of said air gap.

2. A core according to claim 1 in which said tool has bearing means ateach end of said oifset portion, said locating means comprising a firstsupport means positioned on one side of said stack and defining anaperture in alignment with said through hole for engagement with one ofsaid hearing means and a second support means positioned on the oppositeside of said stack and defining an aperture in alignment with saidthrough hole for engagement with the other of said bearing means.

3. A core according to claim 1 in which the apertures of said firstlaminations are slots extending transversely of the direction ofrelative movement of said first laminations and said second laminations,and in which the apertures of said second laminations are circular andhave a diameter which is greater than the width of said slots, saidoffset portion being engaged with the edges of said slots to effect saidrelative movement.

4. A core according to claim 3 in which said offset portion is ofcircular cross-section and constant diameter.

5. A core according to claim 1 in which the apertures of said firstlaminations and said second laminations are of triangular shape, thetriangular apertures of said first laminations having bases positionedopposite to bases of the triangular apertures of said secondlaminations.

6. A core according to claim 5 in which the base of each triangularaperture is disposed parallel to an edge of its respective lamination,the'triangular apertures in said first laminations having their basesdisposed adjacent an outer edge of their respective laminations and thetriangular apertures in said second laminations having their basesdisposed adjacent an inner edge of their respective laminations.

7. In a magnetic circuit a means for varying the reluctance in thecircuit including a ferro-magnetic core of stacked laminations movablerelatively to one another, and

an elongated tool rotatable about its axis and having an offset portionfor efiecting the relative movement between the laminations,

said core comprising,

first laminations each defining a first aperture and a second aperture,and

second laminations interleaved with said first laminations and eachdefining a third aperture and a fourth aperture, the first laminationsco-operating with the second laminations to define an air gap for thecore, the first and third apertures being of identical shape and size,and the second and fourth apertures being of identical shape and size,

locating means for disposing the first laminations and the secondlaminations such that the first apertures and the third apertures are inalignment with the first apertures partially overlapping thethirdapertures to define a first through hole, and such that the secondapertures and the fourth apertures are in alignment with the secondapertures partially overlapping the fourth apertures to define a secondthrough hole of identical shape to-said first through hole, said firstthrough hole and said second through hole being engageable by the offsetportion of said tool to enable said first laminations to be movedrelative to said second laminations.

8. In a magnetic circuit a means for varying the reluctance in thecircuit including a ferromagnetic core of stacked laminations movablerelative to one another, and

an elongated tool rotatable about its axis and having an offset portionfor effecting the relative movement between the laminations with hearingmeans at each end of said ofi'set portion,

said core comprising,

first laminations each defining a series of apertures-of an identicalshape and size, and

second laminations interleaved with said first laminations andco-operating with said first laminations to define an air gap for thecore, and

locating means for aligning said apertures to define a through hole insaid stack for receiving said tool to enable said first laminations tobe moved relative to said second laminations to determine the width ofsaid air gap, said locating means having a first wall on one side ofsaid stack defining an aperture, and having a second wall on theopposite side of said stack defining an aperture, the apertures on saidfirst and second Walls being aligned with said through hole and beingengageable by said bearing means.

References Cited UNITED STATES PATENTS 2,261,323 11/1941 Zierdt 336--234XR 2,930,998 3/1960 Bastian 336- LEWIS H. MYERS, Primary Examiner. T. J.KOZMA, Assistant Examiner.

1. A FERRO-MAGNETIC CORE OF STACKED LAMINATIONS IN COMBINATION WITH ANELONGATED TOOL, SAID STACKED LAMINATIONS BEING MOVABLE RELATIVELY TO ONEANOTHER BY SAID ELONGATED TOOL WHICH IS ROTATABLE ABOUT ITS LONGITUDINALAXIS AND HAS AN OFFSET PORTION FOR EFFECTING RELATIVE MOVEMENT BETWEENTHE LAMINATIONS, SAID CORE COMPRISING FIRST LAMINATIONS EACH DEFINING ANAPERTURE AND ALL BEING IDENTICAL IN SHAPE AND SIZE, AND SECONDLAMINATIONS, INTERLEVED WITH THE FIRST LAMINATIONS, EACH DEFINING ANAPERTURE, AND ALL BEING IDENTICAL IN SHAPE AND SIZE, THE FIRSTLAMINATIONS COOPERATING WITH THE SECOND LAMINATIONS TO DEFINE AN AIR GAPFOR THE CORE, LOCATING MEANS FOR DISPOSING THE FIRST LAMINATIONS SUCHTHAT ALL OF ITS APERTURES ARE IN ALIGNMENT AND FOR DISPOSING THE SECONDLAMINATIONS SUCH THAT ALL OF ITS APERTURES ARE IN ALIGNMENT, THEAPERTURES OF THE FIRST LAMINATIONS PARTIALLY OVERLAPPING THE APERTURESOF THE SECOND LAMINATIONS TO DEFINE A THROUGH HOLE IN THE STACK FORRECEIVING SAID TOOL TO ENABLE THE FIRST LAMINATIONS TO BE MOVED RELATIVETO THE SECOND LAMINATIONS TO ADJUST THE WIDTH OF SAID AIR GAP.